LEP-1a, a new polysaccharide fraction isolated and purified from Lachnum YM40, has a molecular weight of 24.29 kDa. LEP-1a's chemical composition investigation showed that mannose, galactose, and glucose made up the majority of its cosmetics. The methylation, nuclear magnetic resonance, and Fourier transform infrared investigations demonstrated that the (1 → 2)-β-D-Galp, (1 → 2,6)-α-D-Manp, glycosidic connections of LEP-1a were comprised of 1→)-α-D-Manp, (1 → 4)-α-D-Galp, (1 → 6)-α-D-Manp, (1 → 2)-β-D-Glcp, (1 → 4)-β-D-Glcp, (1 → 2)-α-D-Manp, and (1 → 3, 6)-β-D-Manp. LEP-1a has a linear microscopic morphology, as demonstrated by atomic force microscopy, scanning electron microscopy, and rheological property investigation. Moreover, the polysaccharide LEP-1a displayed bile acid- and cholesterol-binding capacities and inhibitory activity on lipase.